Simulation test system for gas extraction from tectonically-deformed coal seam in-situ by depressurizing horizontal well cavity

ABSTRACT

A simulation test system for gas extraction from a tectonically-deformed coal seam in-situ by depressurizing a horizontal well cavity. A coal series stratum structure reconstruction and similar material simulation subsystem simulates a tectonically-deformed coal reservoir. A horizontal well drilling and reaming simulation subsystem constructs a U-shaped well in which a horizontal well adjoins a vertical well, and performs a reaming process on a horizontal section thereof. A horizontal well hole-collapse cavity-construction depressurization excitation simulation subsystem performs pressure-pulse excitation and stress release on the horizontal well, and hydraulically displaces a coal-liquid-gas mixture such that the mixture is conveyed towards a vertical well section. A product lifting simulation subsystem further pulverizes the coal and lifts the mixture. A gas-liquid-solid separation simulation subsystem separates the coal, liquid and gas. A monitoring and control subsystem detects and controls the operation and the execution processes of equipment in real time.

FIELD OF THE INVENTION

The present invention relates to the field of coal seam gas extraction,and relates to a simulation test system for coal seam gas extraction,and in particular, to a simulation test system for gas extraction from atectonically-deformed coal seam in-situ by depressurizing a horizontalwell cavity.

DESCRIPTION OF RELATED ART

Tectonically-deformed coal refers to coal whose coal seam is subject totectonic stress and whose primary structure and construction aresignificantly destroyed due to cracking, resulting in fractures,wrinkles, polished surfaces, and other structural changes. The extensivedevelopment of tectonically-deformed coal and the richness oftectonically-deformed coal seam gas resources are distinguishingfeatures of coal and coal seam gas resources in China.Tectonically-deformed coal resources account for a very high proportionof coal resources that have been discovered in China, and a proportionof a quantity of tectonically-deformed coal seam gas resources to atotal quantity of coal seam gas resources in China is larger.Tectonically-deformed coal has prominent features such as rich gas, lowpermeability, and looseness, and most of tectonically-deformed coal arecoal and gas outburst coal seams. Due to its hazards and difficulty inextraction and utilization, the tectonically-deformed coal is mostlydischarged into the atmosphere in coal production. The efficientdevelopment of tectonically-deformed coal seam gas is of greatsignificance for energy, safety and ecology.

A method based on the theory of hydrophobic depressurization,desorption, and gas recovery is a main method for the development ofsurface wells for in-situ coal seam gas at present. Due to the extremelylow permeability of tectonically-deformed coal reservoirs and the pooreffect of a reconstruction method such as hydraulic fracturing, thetheory of hydrophobic depressurization, desorption, and gas recovery isnot suitable for tectonically-deformed coal reservoirs. The results ofexploration and development practice also show that all coal seam gasexploration and development technologies based on the theory ofhydrophobic depressurization, desorption, and gas recovery, includingSVR technologies (vertical well fracturing, U-shaped well fracturing,multi-branched horizontal well fracturing, horizontal well fracturing,and the like), ECBM technologies (CO₂-ECBM, N₂-ECBM, and the like) andtheir combined technologies, fail to achieve efficient development oftectonically-deformed coal seam gas. Therefore, efficient explorationand development technologies and equipment for tectonically-deformedcoal seam gas have become one of important technical bottlenecksrestricting the rapid and scale development of the China's coal seam gasindustry.

With the in-depth study of coal seam gas extraction technologies, thedevelopment theory of mining-induced pressure relief and permeabilityimprovement for tectonically-deformed coal seam gas in a protected layerin a coal mine area provides a new idea for in-situ extraction oftectonically-deformed coal seam gas. However, in actual extractionapplication, due to the characteristics of tectonically-deformed coal,there are problems such as wellbore fractures caused by overburdendeformation and difficulty in connecting coal to coal seam gasproduction. Therefore, the research and development of a technicaltheory and a simulation test system that are suitable for in-situextraction of tectonically-deformed coal seam gas is an importanttheoretical and practical way to break the technical bottleneck ofefficient development of surface wells for tectonically-deformed coalseam gas in China and realize the exploration and development of coalseam gas in China.

SUMMARY OF THE INVENTION Technical Problem

To resolve the foregoing problem, the present invention provides asimulation test system for gas extraction from a tectonically-deformedcoal seam in-situ by depressurizing a horizontal well cavity, whichenables the simulation of an extraction process including completion ofa large-diameter horizontal well in a loose tectonically-deformed coalreservoir, horizontal well cavity-construction stress release, effectivelifting of mixed fluids, and efficient separation of produced mixtures,thereby providing guidance for efficient and continuous in-situextraction of tectonically-deformed coal seam gas.

Technical Solution

To achieve the foregoing objective, the present invention adopts thefollowing technical solution: a simulation test system for gasextraction from a tectonically-deformed coal seam in-situ bydepressurizing a horizontal well cavity, which comprises a coal seriesstratum structure reconstruction and similar material simulationsubsystem, a horizontal well drilling and reaming simulation subsystem,a horizontal well hole-collapse cavity-construction depressurizationexcitation simulation subsystem, a product lifting simulation subsystem,a gas-liquid-solid separation simulation subsystem, and a monitoring andcontrol subsystem. The coal series stratum structure reconstruction andsimilar material simulation subsystem includes a triaxial stress-tightstereo support, a similar material surrounding rock, a similar materialcoal seam, a high-pressure gas cylinder, and a gas booster pump. Thetriaxial stress-tight stereo support is formed by connecting sixthmovable steel pates to form a sealed hexahedron, in which the similarmaterial surrounding rock and the similar material coal seam aredisposed. Two layers of similar material surrounding rocks arerespectively located above and below the similar material coal seam. AnX-direction servo loading system, a Y-direction servo loading system,and a Z-direction servo loading system are respectively in a hydraulicconnection with a corresponding load piston outside the triaxialstress-tight stereo support. An inlet of the gas booster pump is incommunication with an outlet of the high-pressure gas cylinder, anoutlet pipeline of the gas booster pump is disposed in the similarmaterial coal seam, and a power input port is in communication with anoutlet of an air compressor. A pressure sensor, a temperature sensor,and a strain gauge are disposed in the similar material coal seam near alower end, and are configured to measure a pressure, a temperature, anda strain in the similar material coal seam during a test.

The horizontal well drilling and reaming simulation subsystem includes asimulation drilling rig, a drill column string, a drilling tool, and adrilling fluid circulation system. The drilling tool is a reciprocatingdrilling and reaming tool. The drilling tool, from a connection end withthe drill column string to a drilling end, includes a third-stagereaming and retraction assembly, a primary and secondary reaming andretraction assembly, and a pilot assembly respectively. The third-stagereaming and retraction assembly includes a plurality of expandable andclosable blades that is circumferentially disposed. The blade is lockedand positioned by a second locking mechanism. The primary and secondaryreaming and retraction assembly includes a plurality of extendable andretractable plunger drill bits that is circumferentially disposed. Theplunger drill bit is locked and positioned by a first locking mechanism.The drilling tool is provided with a drill bit positioning sensor and adrilling speed sensor.

The horizontal well hole-collapse cavity-construction depressurizationexcitation simulation subsystem includes a plunger pump, a water tank, apower supply, a measurement device, and an underground injection device.An inlet of the plunger pump is in communication with the water tank,and an outlet of the plunger pump is in communication with theunderground injection device. The underground injection device isdisposed at one side of a horizontal section of the horizontal well neara wellhead. A high level end of the power supply is connected to acopper strip disposed in the horizontal well, and a low level end of thepower supply is connected to a high level end of the measurement device.A low level end of the measurement device is electrically connected to acopper strip on an outer surface of the triaxial stress-tight stereosupport. An underground pressure sensor and a saturation probe aredisposed in the horizontal well near the vertical well. A first pressuresensor are disposed on a liquid inlet pipeline at the wellhead of thehorizontal well.

The product lifting simulation subsystem includes a pulverizationdisturbance device and a hydraulic jet pump. The hydraulic jet pump is awide-flow jet pump and is disposed in the vertical well near the bottomof the well. The pulverization disturbance device is disposed at thebottom of the vertical well and at a joint between the depressurizationcavity and the vertical well.

The gas-liquid-solid separation simulation subsystem includes acoal-liquid-gas separation device, a wastewater collection and treatmentdevice, a coal powder storage device, and a gas collection bottle. Aninlet of the coal-liquid-gas separation device is in communication witha wellhead pipeline of the vertical well, and three outlets of thecoal-liquid-gas separation device are in communication with thewastewater collection and treatment device, the coal powder storagedevice, and the gas collection bottle respectively. A coal-water-gascomponent sensor and a second pressure sensor are disposed on thewellhead pipeline of the vertical well.

The monitoring and control subsystem includes three layers of networkarchitecture and software including on-site workstations, monitoringinstruments and sensors, and a central server control system, and isconfigured to detect and control the operation conditions and theexecution processes of equipment in real time, so as to collect,display, process, and analyze test data.

Further, the horizontal well hole-collapse cavity-constructiondepressurization excitation simulation subsystem further includes anabrasive tank and a mixing chamber. An outlet of the abrasive tank andan outlet of the plunger pump are respectively in communication with themixing chamber. An outlet of the mixing chamber is in communication withthe underground injection device. A branch in communication with thewater tank is disposed on an outlet pipeline of the plunger pump, and apressure regulating valve is disposed on the branch.

Further, the blade on the drilling tool is rotated and opened towardsthe direction of the wellhead of the horizontal well. A drilling fluidoutlet is disposed on the right of the blade, and gradually inclinestowards the direction of the blade when extending towards the outercircumference of the drilling tool from an inner cavity of the drillingtool.

Further, the simulation test system further includes a return waterpump. An inlet of the return water pump is in communication with thewastewater collection and treatment device, and an outlet of the returnwater pump is in communication with the water tank.

Further, a filter is connected between the plunger pump and the watertank.

Further, the strain gauge is a distributed optical fiber measurementinstrument that is longitudinally distributed along the similar materialcoal seam.

Advantageous Effect

In the present invention, based on the similarity principle, the similarsimulation materials with the corresponding physical and mechanicalcharacteristics are configured for the tectonically-deformed coalreservoir; high-pressure gas is injected into the similar material coalseam by means of a high-pressure gas cylinder to simulate geologicalpressure inside the coal seam; and coal seam confining pressure issimulated through three-dimensional loading to the triaxial stress-tightstereo support, to provide a basis for real and accurate simulation ofin-situ extraction of the tectonically-deformed coal seam gas as much aspossible.

In the present invention, the drilling tool in the horizontal welldrilling and reaming subsystem is designed into a three-stage drillingand reaming tool; and further reaming is implemented through two-wayreciprocating drilling construction after drilling in the horizontalsection of the horizontal well. In this way, the diameter of thehorizontal section is greatly increased, the problem of wellborecollapse induced by overburden deformation resulting from the loosetectonically-deformed coal is avoided, and continuous in-situ extractionof tectonically-deformed coal seam gas is ensured.

After the open-hole cavity-constructing completion through reaming ofthe horizontal well, the high-pressure high-speed fluids are injectedinto the horizontal well cavity at a particular pulse frequency tofurther cut and pulverize the medium, to simulate the pressure-pulseexcitation and the stress release on the horizontal well of thetectonically-deformed coal seam gas, and hydraulically displace thecoal-liquid-gas mixture such that the mixture is conveyed towards thevertical well section along the depressurizing space. In this way,subsequent lifting is ensured.

The coal powder is further pulverized and the mixture is lifted towardsthe wellhead of the vertical well through cooperation of the undergroundpulverization disturbance device and hydraulic jet pump; and efficientcoal-liquid-gas separation for the produced mixture and recycling of theexcitation liquid are achieved through the coal-liquid-gas separationdevice.

Real-time detection and control of the operation conditions and theexecution processes of the test equipment are implemented through threelayers of network architecture and software including on-siteworkstations, monitoring instruments and sensors, and a central servercontrol system, so as to collect, display, process, and analyze the testdata. The coordinated operation of subsystems in the entire extractionsystem achieves simulation of efficient and continuous in-situextraction of the tectonically-deformed coal seam gas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall principle diagram of a system of the presentinvention.

FIG. 2 is a schematic diagram of a coal series stratum structurereconstruction and similar material simulation subsystem of the presentinvention.

FIG. 3 is a schematic structural diagram of a drilling tool in thepresent invention.

FIG. 3a is a schematic state diagram of drilling of the drilling tool.

FIG. 3b is a schematic state diagram of reaming of the drilling tool.

FIG. 4 is a schematic diagram of a depressurization excitationsimulation subsystem, a product lifting simulation subsystem, and agas-liquid-solid separation simulation subsystem in the presentinvention.

In the figures: 1: Coal series stratum structure reconstruction andsimilar material simulation subsystem; 1.1: Triaxial stress-tight stereosupport; 1.2: High-pressure gas cylinder; 1.3: Similar materialsurrounding rock; 1.4: Similar material coal seam; 1.5: Z-directionservo loading system; 1.6: Y-direction servo loading system; 1.7:X-direction servo loading system; 1.8: Air compressor; 1.9: Gas boosterpump; 1.10: Load piston; 1.11: Horizontal well; 1.12: Vertical well;1.13: Sixth valve; 2: a horizontal well drilling and reaming simulationsubsystem; 2.1: Pilot assembly; 2.2: Primary and secondary reaming andretraction assembly; 2.3: Third-stage reaming and retraction assembly;2.4: Plunger drill bit; 2.5: Blade; 2.6: Second locking mechanism; 2.7:First locking mechanism; 2.8: Drilling fluid outlet; 3: Horizontal wellhole-collapse cavity-construction depressurization excitation subsystem;3.1: Plunger pump; 3.2: Filter; 3.3: Water tank; 3.4: Pressureregulating valve; 3.5: Abrasive tank; 3.6: Stop valve; 3.7: Mixingchamber; 3.8: First pressure sensor; 3.9: First valve; 3.10: Powersupply; 3.11: Measurement device; 3.12: Underground injection device; 4:Product lifting simulation subsystem; 4.1: Pulverization disturbancedevice; 4.2: Hydraulic jet pump; 5: Gas-liquid-solid separationsimulation subsystem; 5.1: Coal-water-gas component sensor; 5.2: Secondvalve; 5.3: Second pressure sensor; 5.4: Coal-liquid-gas separationdevice; 5.6: Wastewater collection and treatment device; 5.8: Coalpowder storage device; 5.9: Fifth valve; 5.10: Gas collection bottle;5.11: Return water pump; and 6: Depressurization cavity.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is further described below with reference to theaccompanying drawings (a left-right direction in the followingdescription is the same as a left-right direction in FIG. 1).

FIG. 1 to FIG. 4 show a simulation test system for gas extraction from atectonically-deformed coal seam in-situ by depressurizing a horizontalwell cavity, which includes a coal series stratum structurereconstruction and similar material simulation subsystem 1, a horizontalwell drilling and reaming simulation subsystem 2, a horizontal wellhole-collapse cavity-construction depressurization excitation simulationsubsystem 3, a product lifting simulation subsystem 4, agas-liquid-solid separation simulation subsystem 5, and a monitoring andcontrol subsystem. The coal series stratum structure reconstruction andsimilar material simulation subsystem 1 includes a triaxial stress-tightstereo support 1.1, a similar material surrounding rock 1.3, a similarmaterial coal seam 1.4, a high-pressure gas cylinder 1.2, and a gasbooster pump 1.9. The triaxial stress-tight stereo support 1.1 is formedby connecting sixth movable steel pates to form a sealed hexahedron, inwhich the similar material surrounding rock 1.3 and the similar materialcoal seam 1.4 are disposed. Two layers of similar material surroundingrocks 1.3 are respectively located above and below the similar materialcoal seam 1.4 to simulate a coal seam top plate and a coal seam bottomplate. An X-direction servo loading system 1.7, a Y-direction servoloading system 1.6, and a Z-direction servo loading system 1.5 arerespectively in a hydraulic connection with a corresponding load piston1.10 outside the triaxial stress-tight stereo support 1.1, and areconfigured to increase confining pressure for the similar material coalseam 1.4. An inlet of the gas booster pump 1.9 is in communication withan outlet of the high-pressure gas cylinder 1.2, an outlet pipeline ofthe gas booster pump 1.9 is disposed in the similar material coal seam1.4, and a power input port is in communication with an outlet of an aircompressor 1.8, and is configured to increase gas pressure in a coalseam for the similar material coal seam 1.4. A sixth valve 1.13 isdisposed at an outlet of the high-pressure gas cylinder 1.2, and isconfigured to control gas release in the high-pressure gas cylinder 1.2.A pressure sensor (not shown), a temperature sensor (not shown), and astrain gauge (not shown) are disposed in the similar material coal seam1.4 near a lower end, and are configured to measure a pressure, atemperature, and a strain in the similar material coal seam 1.4 during atest.

The horizontal well drilling and reaming simulation subsystem includes asimulation drilling rig (not shown), a drill column string (not shown),a drilling tool, and a drilling fluid circulation system. A connectionbetween the simulation drilling rig and the drill column string is thesame as that in the prior art. The simulation drilling rig is configuredto power the drilling tool. The drill column string is a stringconsisting of a Kelly bar, a drill pipe, a drill collar, and anotherunderground tool, and is configured to install the drilling tool. Thedrilling tool is a reciprocating drilling and reaming tool. The drillingtool, from a connection end with the drill column string to a drillingend, includes a third-stage reaming and retraction assembly 2.3, aprimary and secondary reaming and retraction assembly 2.2, and a pilotassembly 2.1 respectively. The third-stage reaming and retractionassembly 2.3 includes a plurality of expandable and closable blades 2.5that is circumferentially disposed. The blade 2.5 is locked andpositioned by a second locking mechanism 2.6. The primary and secondaryreaming and retraction assembly 2.2 includes a plurality of extendableand retractable plunger drill bits 2.4 that is circumferentiallydisposed. The plunger drill bit 2.4 is locked and positioned by a firstlocking mechanism 2.7. A connection between a drilling fluid positivecirculation system and another component is the same as that in theprior art. The drilling tool is provided with a drill bit positioningsensor and a drilling speed sensor, and is configured to monitor a drillbit position and a drilling speed. During drilling construction of ahorizontal well 1.11, during running towards the direction of a verticalwell 1.12, the plunger drill bit 2.4 is extended to start drilling, andduring returning towards the direction of the simulation drilling rig,the blade 10.5 is opened. Because the diameter after the blade 10.5 isopened is greater than the diameter when the plunger drill bit 10.4 isextended, the horizontal well is reamed, thereby achieving three-stagereaming in rock mass at drillability classes I, II, III, IV and V.Three-stage reaming rates respectively reach 150%, 200%, 300%, and adiameter increase after reaming is 200% to 300%.

The horizontal well hole-collapse cavity-construction depressurizationexcitation simulation subsystem includes a plunger pump 3.1, a watertank 3.3, a power supply 3.10, a measurement device 3.11, and anunderground injection device 3.12. An inlet of the plunger pump 3.1 isin communication with the water tank 3.3, and an outlet of the plungerpump 3.1 is in communication with the underground injection device 3.12.The underground injection device 3.12 is disposed at one side of ahorizontal section of the horizontal well 1.11 near a wellhead. A highlevel end of the power supply 3.10 is connected to a copper stripdisposed in the horizontal well 1.11, and a low level end of the powersupply 3.10 is connected to a high level end of the measurement device3.11. A low level end of the measurement device 3.11 is electricallyconnected to a copper strip on an outer surface of the triaxialstress-tight stereo support 1.1. An underground pressure sensor and asaturation probe are disposed in the horizontal well 1.11 near thevertical well 1.12. A first valve 3.9 and a first pressure sensor 3.8are disposed on a liquid inlet pipeline at the wellhead of thehorizontal well 1.11, and are configured to control injection of anexcitation liquid into the horizontal well 1.11 and monitor injectionpressure. After the open-hole cavity-constructing completion throughreaming of the horizontal well 1.11, the plunger pump 3.1 injectshigh-pressure high-speed fluids to a horizontal well cavity at aparticular pulse frequency, which are sprayed by the undergroundinjection device 3.12 to the horizontal section of the horizontal well1.11 to form a depressurization cavity 6, to implement pressure-pulseexcitation and stress release on the horizontal well oftectonically-deformed coal seam gas; and a gas-liquid-coal mixture isdisplaced through the injected high-pressure high-speed fluids such thatthe mixture is conveyed towards the vertical well 1.12 along adepressurizing space and then produced. A depressurization excitationrange (a stress release area width/a coal thickness) after thepressure-pulse excitation and the stress release are performed on thehorizontal well is ≥15. During depressurization excitation, themeasurement device 3.11 monitors an underground voltage field andcurrent field, and the underground pressure sensor and the saturationprobe measure underground pressure and saturation.

The product lifting simulation subsystem includes a pulverizationdisturbance device 4.1 and a hydraulic jet pump 4.2. The hydraulic jetpump 4.2 is a wide-flow jet pump, is disposed in the vertical well 1.12near the bottom of the well, and is configured to lift thegas-liquid-coal mixture to the wellhead. The pulverization disturbancedevice 4.1 is disposed at the bottom of the vertical well 1.12 and at ajoint between the depressurization cavity 6 and the vertical well 1.12for pulverizing coal powder at the bottom of the well, so that the coalpowder can be more easily lifted by the hydraulic jet pump 4.2 to thewellhead of the vertical well 1.12. In this way, fluids with coal powderconcentration ≤50% are efficiently produced.

The gas-liquid-solid separation simulation subsystem includes acoal-liquid-gas separation device 5.4, a wastewater collection andtreatment device 5.6, a coal powder storage device 5.8, and a gascollection bottle 5.10. An inlet of the coal-liquid-gas separationdevice 5.4 is in communication with a wellhead pipeline of the verticalwell 1.12, and three outlets of the coal-liquid-gas separation device5.4 are in communication with the wastewater collection and treatmentdevice 5.6, the coal powder storage device 5.8, and the gas collectionbottle 5.10 respectively. A second valve 5.2, a coal-water-gas componentsensor 5.1, and a second pressure sensor 5.3 are disposed on thewellhead pipeline of the vertical well 1.12, and are configured tocontrol discharge of the product in the vertical well, and detectcomponents and pressure of the discharged product respectively. Thesubsystem can achieve gas-liquid-coal mixture pre-treating, gasseparation, liquid-coal separation, coal-gas collection, excitationliquid (or water) purification and recycling, with gas separationefficiency of above 90% to 95%, excitation liquid separation andcollection efficiency of above 80% to 90%, and a coal powder collectioncapability of above 98%.

The monitoring and control subsystem includes three layers of networkarchitecture and software including on-site workstations, monitoringinstruments and sensors, and a central server control system. Based on ahigh-precision sensor technology, through construction of the threelayers of network architecture including the sensors, the on-siteworkstations, and the central server control system, and application ofa database technology and a filtering algorithm, real-time storage andhigh-precision processing of mass data are implemented; an intelligentalgorithm is used to implement closed loop control of physicalparameters of a test platform; and configuration analysis software andan Internet of Things perception technology are applied, to form a dataacquisition and monitoring system that is “accurate, visual,interactive, fast, and intelligent” to detect and control the operationconditions and the execution processes of the test system in real time,so as to collect, display, process, and analyze engineering data.

As shown in FIG. 1 and FIG. 4, the horizontal well hole-collapsecavity-construction depressurization excitation simulation subsystemfurther includes an abrasive tank 3.5 and a mixing chamber 3.7. Anoutlet of the abrasive tank 3.5 and an outlet of the plunger pump 3.1are respectively in communication with the mixing chamber 3.7. An outletof the mixing chamber 3.7 is in communication with the undergroundinjection device 3.12. The addition of a particular proportion of anabrasive to the excitation liquid improves the capability of theexcitation liquid to cut a coal rock, thereby improving extractionefficiency. A stop valve 3.5 is disposed at the outlet of the abrasivetank 3.5, and is configured to control abrasive input to the mixingchamber 3.7. A branch in communication with the water tank 3.3 isdisposed on an outlet pipeline of the plunger pump 3.1, and a pressureregulating valve 3.4 is disposed on the branch, and is configured tocontrol pressure of the excitation liquid.

As shown in FIG. 1, FIG. 3 a, and FIG. 3 b, the blade 2.5 on thedrilling tool is rotated and opened towards the direction of thewellhead of the horizontal well. A drilling fluid outlet 2.8 is disposedon the right of the blade 2.5, and gradually inclines towards thedirection of the blade 2.5 when extending towards the outercircumference of the drilling tool from an inner cavity of the drillingtool. During drilling, drilling fluids can achieve cooling and auxiliarycutting functions like conventional drilling fluids, and can alsoprovide sufficient support for the expansion of the blade 2.5, to reducerigid deformation of a connecting member with the blade 2.5, and prolonga service life of the device.

As shown in FIG. 1 and FIG. 4, the simulation test system furtherincludes a return water pump 5.11. An inlet of the return water pump5.11 is in communication with the wastewater collection and treatmentdevice 5.6, and an outlet of the return water pump 5.11 is incommunication with the water tank 3.3. Separated excitation liquid istreated and then enters the water tank 3.3 for recycling, therebyensuring continuity of the test and saving resources.

A filter 3.2 is connected between the plunger pump 3.1 and the watertank 3.3, and is configured to filter out impurities in water that flowsfrom the water tank 3.3 into the plunger pump 3.1, to prevent impuritiesin recycling water from damaging the plunger pump 3.1.

The strain gauge is preferably a distributed optical fiber measurementinstrument that can be longitudinally distributed along the similarmaterial coal seam 1.4, so that measured strain data is more accurate.

The specific test process includes the following steps:

1) according to actual geological characteristics of atectonically-deformed coal reservoir and based on a similarityprinciple, configuring similar simulation materials with correspondingphysical and mechanical characteristics, disposing the similarsimulation materials in a triaxial stress-tight stereo support 1.1, andarranging a stress sensor, a temperature sensor, and a strain gauge.

Preheating the triaxial stress-tight stereo support 1.1 in a constanttemperature room to reach a test design temperature.

Opening a sixth valve 1.13, starting an air compressor 1.8 and a gasbooster pump 1.9, injecting gas into a similar material coal seam 1.4,starting an X-direction servo loading system, a Y-direction servoloading system, and a Z-direction servo loading system, increasing aconfining pressure to a test design pressure for the triaxialstress-tight stereo support 1.1, checking the airtightness of thedevice; and if the airtightness meets a requirement, performing a nextstep; or if the airtightness does not meet a requirement, repeating thisstep.

2) Arranging various devices and connecting the corresponding devices,and using an existing drilling tool and processing technology toconstruct vertical well sections and kick-off sections of a verticalwell 1.12 and a horizontal well 1.11 to the similar material coal seam1.4, where a drilling fluid circulation system provides drilling fluidsfor the underground during construction.

3) Replacing the drilling tool with a reciprocating drilling and reamingtool and lowering the reciprocating drilling and reaming tool to thekick-off section of the horizontal well, performing three-stage reamingand large-diameter well completion on the similar material coal seam1.4, and forming a horizontal well section that runs through thevertical well 1.12 (forming a U-shaped well in which the horizontal welladjoins the vertical well), to achieve open-hole cavity-constructingcompletion, where the drilling fluid circulation system provides thedrilling fluids for the underground during construction.

4) Removing all drilling tools from the well, and lowering anunderground injection device 3.12 and a copper strip connected to a highlevel end of a power supply 3.10 to a starting point of the horizontalsection of the horizontal well 1.11, lowering gas-liquid-coal mixturelifting and production devices, namely, a pulverization disturbancedevice 4.1 and a hydraulic jet pump 4.2 to the vertical well 1.12, andconnecting a wellhead of the vertical well 1.12 to a coal-liquid-gasseparation device 5.4.

5) Opening a first valve 3.9, starting a plunger pump 3.1, injectinghigh-pressure high-speed fluids into the horizontal section of thehorizontal well 1.11 at a specified frequency, to cut and pulverize acoal rock and implement pressure-pulse excitation and stress release onthe horizontal section of the horizontal well 1.11 to form adepressurization cavity 6, then accelerating water into high-velocityjet flows, to further pulverize and flush coal powder, and conveying aformed gas-liquid-coal mixture to the bottom of the vertical well 1.12,where during the pressure-pulse excitation and the stress release on thehorizontal section of the horizontal well 1.11, a particular proportionof an abrasive may be mixed in the excitation liquid to improve thecapability of the excitation liquid to cut a coal rock, therebyimproving extraction efficiency.

6) Opening a second valve 5.2 and a fifth valve 5.9, starting theunderground pulverization disturbance device 4.1 and hydraulic jet pump4.2, further pulverizing the coal powder that flows into the bottom ofthe vertical well 1.12, and then lifting the coal powder to the groundto enter the coal-liquid-gas separation device 5.4.

7) Separating the mixture that enters the coal-liquid-gas separationdevice 5.4, and allowing coal seam gas, an excitation liquid, and coalpowder that are separated to respectively enter a gas collection bottle5.10, a wastewater collection and treatment device 5.6, and a coalpowder storage device.

8) Starting a return water pump 5.11 and transferring the treatedexcitation liquid to a water tank 3.3 for recycling.

The monitoring and control simulation subsystem collects correspondingrelated data such as a time, pressure, a temperature, stress-strain,saturation, a voltage/current, sedimentation solid mass, produced liquidmass, and a produced gas flow while controlling the foregoing respectivesteps, and records the data as a data file.

1. A simulation test system for gas extraction from atectonically-deformed coal seam in-situ by depressurizing a horizontalwell cavity, comprising a coal series stratum structure reconstructionand similar material simulation subsystem, a horizontal well drillingand reaming simulation subsystem, a horizontal well hole-collapsecavity-construction depressurization excitation simulation subsystem, aproduct lifting simulation subsystem, a gas-liquid-solid separationsimulation subsystem, and a monitoring and control subsystem, whereinthe coal series stratum structure reconstruction and similar materialsimulation subsystem includes a triaxial stress-tight stereo support, asimilar material surrounding rock, a similar material coal seam, ahigh-pressure gas cylinder, and a gas booster pump, the triaxialstress-tight stereo support is formed by connecting sixth movable steelpates to form a sealed hexahedron, in which the similar materialsurrounding rock and the similar material coal seam are disposed, twolayers of similar material surrounding rocks are respectively locatedabove and below the similar material coal seam, an X-direction servoloading system, a Y-direction servo loading system, and a Z-directionservo loading system are respectively in a hydraulic connection with acorresponding load piston outside the triaxial stress-tight stereosupport; an inlet of the gas booster pump is in communication with anoutlet of the high-pressure gas cylinder, an outlet pipeline of the gasbooster pump is disposed in the similar material coal seam, and a powerinput port is in communication with an outlet of an air compressor; apressure sensor, a temperature sensor, and a strain gauge are disposedin the similar material coal seam near a lower end, and are configuredto measure a pressure, a temperature, and a strain in the similarmaterial coal seam during a test; the horizontal well drilling andreaming simulation subsystem includes a simulation drilling rig, a drillcolumn string, a drilling tool, and a drilling fluid circulation system,the drilling tool is a reciprocating drilling and reaming tool, thedrilling tool, from a connection end with the drill column string to adrilling end, includes a third-stage reaming and retraction assembly, aprimary and secondary reaming and retraction assembly, and a pilotassembly respectively, the third-stage reaming and retraction assemblyincludes a plurality of expandable and closable blades that iscircumferentially disposed, the blade is locked and positioned by asecond locking mechanism, the primary and secondary reaming andretraction assembly includes a plurality of extendable and retractableplunger drill bits that is circumferentially disposed, the plunger drillbit is locked and positioned by a first locking mechanism; the drillingtool is provided with a drill bit positioning sensor and a drillingspeed sensor; the horizontal well hole-collapse cavity-constructiondepressurization excitation simulation subsystem includes a plungerpump, a water tank, a power supply, a measurement device, and anunderground injection device, an inlet of the plunger pump is incommunication with the water tank, and an outlet of the plunger pump isin communication with the underground injection device, the undergroundinjection device is disposed at one side of a horizontal section of thehorizontal well near a wellhead; a high level end of the power supply isconnected to a copper strip disposed in the horizontal well, and a lowlevel end of the power supply is connected to a high level end of themeasurement device, a low level end of the measurement device iselectrically connected to another one copper strip on an outer surfaceof the triaxial stress-tight stereo support; an underground pressuresensor and a saturation probe are disposed in the horizontal well nearthe vertical well; a first pressure sensor are disposed on a liquidinlet pipeline at the wellhead of the horizontal well; the productlifting simulation subsystem includes a pulverization disturbance deviceand a hydraulic jet pump, the hydraulic jet pump is a wide-flow jet pumpand is disposed in the vertical well near a bottom of the vertical well;the pulverization disturbance device is disposed at the bottom of thevertical well and at a joint between the depressurization cavity and thevertical well; the gas-liquid-solid separation simulation subsystemincludes a coal-liquid-gas separation device, a wastewater collectionand treatment device, a coal powder storage device, and a gas collectionbottle, an inlet of the coal-liquid-gas separation device is incommunication with a wellhead pipeline of the vertical well, and threeoutlets of the coal-liquid-gas separation device are in communicationwith the wastewater collection and treatment device, the coal powderstorage device, and the gas collection bottle respectively; acoal-water-gas component sensor and a second pressure sensor aredisposed on the wellhead pipeline of the vertical well; the monitoringand control subsystem includes three layers of network architecture andsoftware including on-site workstations, monitoring instruments andsensors, and a central server control system, and is configured todetect and control operation conditions and execution processes ofequipment in real time, so as to collect, display, process, and analyzetest data.
 2. The simulation test system for gas extraction from atectonically-deformed coal seam in-situ by depressurizing a horizontalwell cavity according to claim 1, wherein the horizontal wellhole-collapse cavity-construction depressurization excitation simulationsubsystem further includes an abrasive tank and a mixing chamber, anoutlet of the abrasive tank and the outlet of the plunger pump arerespectively in communication with the mixing chamber, an outlet of themixing chamber is in communication with the underground injectiondevice; a branch in communication with the water tank is disposed on anoutlet pipeline of the plunger pump, and a pressure regulating valve isdisposed on the branch.
 3. The simulation test system for gas extractionfrom a tectonically-deformed coal seam in-situ by depressurizing ahorizontal well cavity according to claim 1, wherein the blade on thedrilling tool is rotated and opened towards a direction of the wellheadof the horizontal well, and a drilling fluid outlet is disposed on theright of the blade, and gradually inclines towards a direction of theblade when extending towards the outer circumference of the drillingtool from an inner cavity of the drilling tool.
 4. The simulation testsystem for gas extraction from a tectonically-deformed coal seam in-situby depressurizing a horizontal well cavity according to claim 3, whereinthe simulation test system further includes a return water pump, aninlet of the return water pump is in communication with the wastewatercollection and treatment device, and an outlet of the return water pumpis in communication with the water tank.
 5. The simulation test systemfor gas extraction from a tectonically-deformed coal seam in-situ bydepressurizing a horizontal well cavity according to claim 3, wherein afilter is connected between the plunger pump and the water tank.
 6. Thesimulation test system for gas extraction from a tectonically-deformedcoal seam in-situ by depressurizing a horizontal well cavity accordingto claim 3, wherein the strain gauge is a distributed optical fibermeasurement instrument that is longitudinally distributed along thesimilar material coal seam.